As a native speaker, my first thought was: you're right.
"Sie fegte über die Bühne." translates as "She ran across the stage.", which describes a movement like "Sie ist gelaufen" ("She walked"). Whereas the second "Sie fegte die Bühne" means - as you wrote - "She swept the stage", which is more of a crafting act like "She painted the stage" ("Sie hat die Bühne gestrichen").